The neural connections and mechanisms underlying rhythmic motor patterns is at present not known. In an effort to understand these mechanisms, and invertebrate model system, the lobster stomatogastric ganglion can be used to study the genesis of rhythmic motor patterns. This ganglion of only 30 cells produces two separate rhythms in isolated and completely deafferented preparation. THe neural circuitry underlying both patterns has been determined. Using a new dye-sensitized photoinactivation technique, the mechanisms for the production of the pyloric rhythm have been elucidated. This proposal is to complete an analysis of the gastric system using the same experimental technique, but in a more quantitative manner. We have formulated a tentative hypothesis for the gastric mechanism which allows us to predict the consequences of particular cell deletions. These will be experimentally tested and the hypothesis modified as required. In addition we will begin an examination of the sensory control of the stomatogastric pattern generation and the effects of the neuromodulatory substances neurodepressing hormone from the eyestalk; serotonin and octopamine, which are found in the stomatogastric system.